Edit: As suggested by Rory Alsop in the comments, I believe this question is not a duplicate of:

Performance Exhaust -- what, how, why?


Exhaust Backpressure and Its Impact on LTFT Values

I read these questions prior to asking mine, they don't seem to be talking about super chargers specifically. They do mention that performance gains are limited when considering a new exhaust but I'm specifically asking about a scenario with FI and a stock exhaust. For example, swapping out a 2" exhaust to a 3" exhaust isn't going to give you much of a HP increase, but will adding 12 psi of boost on a 2" exhaust limit the amount of HP you'll receive, because the 2" exhaust is limiting the amount the engine can work (too much back pressure).

I've tried to read up a lot on the affects of super chargers on exhausts but a lot of the information I've found has been from mismatched forums so forgive me if my info is completely off.

I know the title question highly depends on the amount of boost, size of your engine, and size of your stock exhaust. In my case my car is a 2018 Subaru BRZ but for the sake of keeping the question general I'd like to consider any generic stock exhaust for a car with about 200hp.

Essentially, I'm wondering if an exhaust is 2" and below at any point from the engine to the mufflers will this limit how much power you can get out of a super charger?

I'm under the impression that with a turbo charger this can definitely affect performance because the turbo runs off the amount of exhaust that can flow out of the car. I've also heard that "super chargers like to breath too" and that for most FI systems you'll want at least 2.5" of exhaust diameter.

Specifically in my case, I'm considering a 2.3" cat back exhaust (allegedly rated for up to 350hp), with the potential to super charge later up to ~300hp. I'm wondering whether I'll need to replace the rest of the exhaust to reach the 300 mark.

  • Have you read the Related questions in the sidebar to the right? Especially mechanics.stackexchange.com/q/4086/37 and mechanics.stackexchange.com/questions/24675/37 - they may already have the answer for you. – Rory Alsop Mar 26 '19 at 17:30
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    Possible duplicate of Performance Exhaust -- what, how, why? – Rory Alsop Mar 26 '19 at 17:30
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    While I don't know exactly how you figure it all out, the simple answer is "yes", your stock exhaust can limit gains. To what extent depends on how the exhaust was constructed. Things like crimped bends and small tubes make a big play here. Considering an ICE is basically an air pump, getting air in and exhaust out is how you make horsepower. If the exhaust limits the amount of flow, it will limit the amount of HP which can be made. Stock exhaust is made to support a stock engine. Start throwing FI at it and you'll soon max out its capacity to move air. – Pᴀᴜʟsᴛᴇʀ2 Mar 26 '19 at 17:52
  • @RoryAlsop Thanks for the suggestion, I've updated the question to explain why I believe this not to be a duplicate of the ones you posted – Paul Warnick Mar 26 '19 at 18:09
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    Unless you can find someone who has dyno tested (accurately; also type of dyno dependent), you're really not going to know for sure. You need empirical data to really know. If you don't have the data, it's all conjecture. I've not seen anything for the BRZ. Just because someone stated it has a "sport like design" means absolutely nothing. There are very few stock exhaust designs which lend to flow. They are about getting the exhaust out the back of the vehicle, keeping it quiet while doing so, and keeping it out of the passenger cabin ... not making more power. – Pᴀᴜʟsᴛᴇʀ2 Mar 26 '19 at 18:18

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